MySQL:最简单，也是最容易犯错的sql问题

原始sql如下：

mysql> select * from gso  WHERE express_generation_sn = 160425135761159  LIMIT 1; 
1 row in set (1.15 sec)

mysql> explain select * from gso  WHERE express_generation_sn = 160425135761159  LIMIT 1;
+----+-------------+----------------+------+-----------------------+------+---------+------+--------+-------------+
| id | select_type | table          | type | possible_keys         | key  | key_len | ref  | rows   | Extra       |
+----+-------------+----------------+------+-----------------------+------+---------+------+--------+-------------+
|  1 | SIMPLE      | gso            | ALL  | express_generation_sn | NULL | NULL    | NULL | 390755 | Using where |
+----+-------------+----------------+------+-----------------------+------+---------+------+--------+-------------+
1 row in set (0.00 sec)

相当简单的sql执行需要1.15s

原因：

mysql> select * from gso  WHERE express_generation_sn = '160425135761159'  LIMIT 1;
1 row in set (0.00 sec)

mysql> explain select * from gso  WHERE express_generation_sn = '160425135761159'  LIMIT 1;
+----+-------------+----------------+------+-----------------------+-----------------------+---------+-------+------+-------------+
| id | select_type | table          | type | possible_keys         | key                   | key_len | ref   | rows | Extra       |
+----+-------------+----------------+------+-----------------------+-----------------------+---------+-------+------+-------------+
|  1 | SIMPLE      | gso            | ref  | express_generation_sn | express_generation_sn | 153     | const |    1 | Using where |
+----+-------------+----------------+------+-----------------------+-----------------------+---------+-------+------+-------------+
1 row in set (0.00 sec)

到这里一眼也就知道拉，express_generation_sn 是varchar类型，所以开发规范很重要！！

也知道不是所有带sn，num的都是数字字段，不能想当然